MOT is tomorrow so I set about fixing it myself today and as I couldn't find a how-to online I thought I should get this on here now I've managed to sort it with relative ease, especially with this being a common error from what I've read.WHAT YOU'LL NEED...
Torx key for the four mounting bolts
Multimeter
Thin flat head screwdrivers
Soldering iron and solder
Piece of electrical wire
*Black silicone*
TIME...
1-2HOURS
HOW TO FIX...
1. Locate the license plate bulbs, pry out the plastic covers and try to replace them. If it works great, it not then continue...
2. Check for voltage to each of the bulb holders using the multimeter (obviously you need to switch your lights on for this). If it's like mine one will be recieving around 11 volts and the other zero. I set the multimeter to 20v setting for this.
3. Remove the black strip that contains the lights from the car by undoing the four torx bolts... Then unclip the wiring harness.
4. View the back of the strip... It's not particularly designed to be stripped apart but a flathead screwdriver or two can help separate the long black back piece that looks like it's been sealed to contain the wiring. Seems daunting at first but if it's like mine I thought it's broke anyway so what do I have to lose!
5. Reveal the wiring /circuit board... I tried to clean the contacts etc but it did no good. The circuit board can be carefully pried out. Examine the board and find four wires from the connector, two little buttons for the boot unlock and the two light bulb holders. It's a very simple set up.
6. Use the multimeter on the continuity setting (the one which makes a beep if two things are connected) to explore which wire connects to which part of each light terminal. I found that one of the brown wires connected to the outer most parts of the light fittings and one of the grey wires connected to ONE of the innermost light fittings but had no continuity to the other... This was clearly my issue!
7. Use the soldering iron to connect the right wire to the right part of the light fitting that was missing the continuity using some electrical wire. This is very basic and doesn't need to be a work of art as it will be concealed. Check for continuity between the the wire and the desired end of the light holder using the multimeter.
8. Reassemble. At this stage it might be worth siliconing the plastic cover back on to seal it from the weather (I've not had chance to do this yet but I will have to prioritise this or I'm sure I'll end up with bigger problems).
9. Re-connect at the car and screw the fitting back on.
10. Turn on the lights and feel good about saving a decent amount of money!
I do have images for this but don't can't find a button to upload directly to here. It's simple enough once you figure out which wire leads to which end of the light terminals (the other two wires are for the bootlid button). Saying this, I imagine this could provide a similar procedure for if your bootlid button stops working from a faulty connection too.
Anyway... I'm not a regular on the forum these days so doubt i'll be on much to answer questions etc but I hope this is helpful for some e53 drivers in the future
Never anthropomorphise computers. They hate that.